In a fuel pump module which is accommodated in a fuel tank of automobiles and the like and plays a role of supplying fuel to an internal-combustion engine, a large part of the tubes for transporting fuel mounted in the module is immersed into fuel in the fuel tank (for example, cf. PTL 1). Therefore, in the tube for transporting fuel, both its innermost layer and outermost layer are directly contacted with the fuel, and fuel resistance is required for both sides. Hence, for the tube for transporting fuel, a resin composition containing resin such as polyamide 11 and polyamide 12, which is excellent in fuel resistance and a fuel penetration preventing property, is used.
In recent years, from the viewpoint of reduction in greenhouse gases, fuel derived from biomass has begun to be used for fuel of automobiles and the like. In diesel engine vehicles, fuel containing FAME (Fatty Acid Methyl Ester) obtained by transesterifying vegetable oil with methanol to separate and remove glycerol is used as a “biodiesel fuel”. Examples of FAME include mixed fatty acid methyl ester containing unsaturated fatty acid methyl ester, etc. such as RME (Rapeseed Methyl Ester) derived from rapeseed oil, SME (Soybean Methyl Ester) derived from soybean, SFME (Sunflower Methyl Ester) derived from sunflower oil, PME (Palm Methyl Ester) derived from palm oil, and JME derived from jatropha oil (Jatropha Methyl Ester).
However, the fuel containing FAME containing unsaturated fatty acid methyl ester easily generates decomposed matters such as peroxides, carboxylic acid, alcohols, ketones and aldehydes by oxidization of a double bond portion or hydrolysis of an ester bond. These decomposed matters cause degradation of a resin composition in contact with fuel. Therefore, the resistance required for the resin composition in contact with biodiesel fuel is essentially different from resistance of conventional fuels such as gasoline and light oil, and a resin composition which is conventionally regarded as being excellent in fuel resistance cannot be always applied as it is.
PTL 2 discloses that a molding member comprising polyamide resin, in which: a dicarboxylic acid component comprises oxalic acid; a diamine component comprises 1,9-nonanediamine and 2-methyl 1,8-octanediamine; and a molar ratio of 1,9-nonanediamine and 2-methyl 1,8-octanediamine is 1:99 to 99:1, is excellent in biodiesel resistance and the like. However, when the molding member is a tube, elongation properties are inferior and a crack may occur when inserted into other members such as a quick connector.
PTL 3 discloses that a multilayer hose for transporting high-temperature liquid and/or gas chemicals comprising a layer comprising an aliphatic polyamide and a layer comprising a semi-aromatic polyamide having a specific structure is excellent in chemical resistance. However, it is not assumed that the multilayer hose is used in the environment in which both its innermost layer and outermost layer are contacted with biodiesel fuel.